Geographic Variation Four subspecies show weak to moderate variation. Bird’s overall size and the extent of white in its wings and tail decline from the northern part of the range to the Gulf Coast; bill, leg, and foot sizes increase. The large nominate subspecies (breeds in North) has red irides, most extensive white in tail. Smaller alleni of Florida paler and duller, with straw-colored irides. Intermediate southern subspecies canaster (west) and rileyi (east) have variably orange to straw-colored irides.